Irate lawmakers today accused the acting IRS commissioner of misleading them about the agency's selective scrutiny of tea party-affiliated groups, demanding to know who was responsible and why no one told Congress about it.

"Why did you mislead Congress and the American people on this?" Louisiana GOP Rep. Charles Boustany, who chairs the Ways and Means panel's Oversight Subcommittee, asked Steven Miller.

Miller apologized but maintained that politics did not motivate the perceived targeting.

"First and foremost, as acting commissioner I want to apologize on behalf of the IRS for the mistakes that we made and the poor service that [we] provided," Miller told the House Ways and Means Committee in his opening statement. "Partisanship or even the perception of partisanship has no place at the IRS."

Miller has effectively been fired by the Obama administration. Treasury Secretary Jack Lew requested his resignation, but Miller remains acting commissioner until his appointment expires June 8.

"I think that what happened here is that foolish mistakes were made by people who were trying to be more efficient in their workload selection," Miller told the committee.

Asked by Georgia GOP Rep. Tom Price whether he thinks the IRS's actions were "illegal," the outgoing commissioner said it is not.

"It is absolutely not illegal," Miller told Price.

Miller asked Price to clarify his question, which Price did: "Do you believe it is illegal for employees of the IRS to create lists to target individual groups and citizens in this country," the conservative congressman asked Miller.

"I don't believe it is. I don't believe it should happen," Miller said, after indicating that the legality of the IRS' practices is for others to decide.

Committee members grilled Miller on who at the IRS knew what, and when. Miller said that after initially becoming aware of problems last year with conservative groups' 501(c)4 applications, he asked an IRS official "to lead a team and take a look and see what was going on in terms of cases that had gotten those letters."

One employee was reassigned, and managers were instructed that the targeting should not continue, Miller said.

Rep. Paul Ryan, R-Wis., asked Miller why he failed to mention it in July 2012, when he appeared before a subcommittee hearing and was asked about conservative groups' difficulties with the IRS.

"How can we not conclude that you misled this committee?" Ryan asked. "You knew of our concern of this targeting … You knew that, but you didn't mention this to the committee. Do you not think that that's a very incomplete answer?"

Miller said he didn't mention the actions because the question had implied political motivation, which he did not believe existed. Miller said he was only asked about letters from conservative groups.

"I did not mislead the committee. I stand by my answer then, and I stand by my answer now," Miller said. "Harassment that was part of that question implies political motivation."

At a July 25, 2012 subcommittee hearing on tax-exempt organizations, Texas GOP Rep. Kenny Marchant asked Miller about conservative groups that had complained of IRS scrutiny.

"I have been contacted by several of the groups in my district. And they feel like they are being harassed. I don't have any evidence that that is the case.

"But they feel like they have been harassed and feel like the IRS is threatening them with some kind of action or audit. What kind of a letter or action is taking place at this time that you are aware of?" Marchant asked Miller at that hearing, after Miller had been briefed on the scrutiny of tea party groups.

Miller responded, at the time, without mentioning the actions of which he now says he was aware.

"I am aware that there is an uptick of organizations that came into us for exemption," Miller said in July 2012. "So it was the determination letter process, not the examination process. I am aware that some 200 501(c)4 applications fell into this category. We did group those organizations together to ensure consistency, to ensure quality. We continue to work those cases."

"Because she's a superb civil servant, sir," Miller explained, noting that he did not think Ingram was involved in the scrutiny of tea party groups.

In the course of asking extra questions of tea party groups, IRS officials requested lists of their donors. Miller told the committee today that he believes the agency destroyed those lists.

Miller also defended former commissioner Douglas Shulman's testimony in March 2012 that "there's absolutely no targeting," explaining that at that time, he and Shulman were aware of problems with conservative groups' processing, but not that keywords and groups' policy missions were being used to single them out.

"It was incorrect, but whether it was untruthful or not -- look, when you talk about targeting … it's a pejorative term," Miller said. "What happened here is that someone saw tea party cases come through, they were acknowledging that they were going to be engaged in politics. This is the time frame in 2010 when Citizens United was happening … people in Cincinnati decided, 'Let's centralize these cases.'"

Miller took issue with the term "targeting" multiple times.

"Again, I'm going to take exception to the term 'targeting,'" Miller said when Texas GOP Rep. Kevin Brady asked him, directly, who was responsible.

Miller said he prefers the term "listing" and that he didn't have any names of IRS employees to supply.

Both Republican and Democratic members voiced frustration with the activities, by any name, that Miller and others failed to mention to Congress before now.